We will study the effects of frontotemporal lobar degeneration (FTLD), Alzheimer's disease (AD), and mild cognitive impairment (MCI) on socioemotional functioning using laboratory procedures that allow for precise assessment of a number of aspects of actual emotional functioning including: (a) emotional reactivity (the type and magnitude of responses to salient challenges and opportunities), (b) emotion regulation (the ability to adjust emotional responses to situational demands) and (c) empathy and prosocial behavior (recognizing others' emotions and responding to their distress). These laboratory-based assessments measure the major aspects of emotional responding, including: (a) subjective emotional experience, (b) emotional expressive behavior, (c) emotional language, and (d) autonomic and somatic nervous system physiology. This approach allows us to identify specific areas of lost and preserved socioemotional functioning in FTLD and AD, compared to each other and to MCI and controls. A particular focus of the proposed work is on understanding the basis of symptoms of FTLD that are very troublesome for caregivers, including a progressive loss of warmth and an increase in socially inappropropriate behavior. We will use our detailed analyses of emotional functioning to explore the particular deficits that contribute to these real world symptoms. Delineating specific deficits will enable us to make strong links to damage in specific brain circuits (explored via structural imaging) and particular kinds of neuropathology (explored at autopsy). In addition, we will determine the extent to which changes in particular aspects of socioemotional functioning are related to genetic risk factors for FTLD by studying unaffected family members with and without suspected genetic markers in families with a high incidence of FTLD.